Electrical power cables are widely used for distributing power across vast power grids or networks, moving electricity from power generation plants to the consumers of electric power. Power cables may be constructed to carry high voltages (greater than about 50,000 Volts), medium voltages (between about 1,000 Volts and about 50,000 Volts), or low voltages (less than about 1,000 Volts).
As power cables are routed across the power grids to the consumers of electric power, it is often necessary or desirable to periodically terminate the electrical cable for making a connection to electrical equipment. Typically, a termination is used to make electrical connection between the insulated electrical cable and an unshielded, un-insulated conductor. The termination fits over an end of the insulated cable.
A cable termination of the electrical cable creates an abrupt discontinuity in the electrical characteristics of the cable. The discontinuity changes the shape of the resulting electrical field and electrical stress so as to increase the risk of insulation breaking down. Thus, one function of a cable termination, among others, is to compensate for the change in electrical field and electrical stress generated when there is a discontinuity in the electrical cable. The cable termination also functions to protect the terminated end portion from the ambient conditions.
With respect to medium voltage (MV) terminations, it is necessary to control electrical field stresses built up at the locations of splices and terminations. Generally, there are two ways to achieve such a control. The first way is to apply a stress cone, as disclosed in U.S. Pat. No. 7,251,881B2, wherein the termination is relatively large and two steps of molding are needed. The second way is to apply a stress control tube of stress relief material. However, since the traditional stress relief material has a high dielectric constant but a poor dielectric strength, two layers are needed for a cable termination. One layer is made of a material with a high dielectric constant, which provides an electrical stress relief function, and another layer is made of an insulating material for insulation which covers on the outside of the layer of high dielectric constant. As a result, the two layers need to be produced and installed separately, leading to a complex procedure and a higher cost.
Cold shrink technology offers easy installation and reliable performance when terminating indoor and outdoor medium voltage cables. For cold shrink tubes used for cable terminations, the mechanical property, especially elongation at break, is critical for the application. Further, in order to be used as one layer tube for a termination, the material for the tube should have a high volume resistivity.
Therefore, there is a need to develop an insulating composition having a satisfactory dielectric constant suitable to make an electrical cable accessory, for example, cable terminations of at least MV electrical cable.